should do the trick. I'm assuming your windows desktop resolution is set to 1080p? If so, it should work. 0x0 tells DOSBox to use whatever your desktop is set to.
Can you do that in the dosbox interface that GOG gives you? Or do you have to edit the configuration file directly?
Directly, GOG's config program doesn't seem to have an option to edit the fullscreen resolution, just the windowed res.
While you've got the config file open, KingofGnG's suggestions are good:
aspect=true will make sure the game is 4:3 even if it used a non-square pixel mode.
As for the scaler setting, it's a pretty subjective thing, but given that your screen is 1080 pixels tall I'd go for one of the 3x scalers (e.g. normal3x, advmame3x, hq3x).